providing ACL fails with SignatureDoesNotMatch

## Summary

When uploading a file to Storage (S3 or DigitalOcean Spaces), with the ACL header/parameter, the request fails with "SignatureDoesNotMatch" exception.

## Detailed Information
Demo code:
```py
container = ...
src = 'somefile.txt'
dst = 'somewhere/somefile.txt'
extra = {'acl': 'public-read'}
obj = driver.upload_object(src, container, dst, extra=extra)
```

Providing meta_data, and/or other information in the `extra` dict works just fine, it fails as soon as I provide any `acl` key/value.

- Libcloud version: 3.3.1
- Python version: 3.9.1

**Screenshots:**

AWS S3:


DigitalOcean Spaces:

Start at the storage driver's upload_object entry point and trace how the extra dictionary is handled for S3 and DigitalOcean Spaces. Reproduce the supplied upload with extra={'acl': 'public-read'} and compare it with metadata-only uploads, then verify that ACL requests no longer fail with SignatureDoesNotMatch.

Written by the indexing model from the issue text.